Diterpenoids with diverse scaffolds from Vitex trifolia as potential topoisomerase I inhibitor.

Eleven new compounds, including six labdane (1-6), three halimane (7-9), and two clerodane (10-11) diterpenoids and 16 known analogues (12-27), were isolated from the leaves of Vitex trifolia. The structures of 1-11 were established by extensive 1D- and 2D-NMR and HRMS spectroscopic data. The absolute configurations of compounds 3, 7, and 10 were assigned using X-ray diffraction. Compounds 1-27 were evaluated for DNA topoisomerases I (Top1) inhibitory activity and cytotoxicity against HCT 116 cells. Compounds 8 and 11 exhibited equipotent Top1 inhibitory activity to the positive control, camptothecin (CPT), at 100μM. Compounds 8, 9, 16, and 27 showed moderate cytotoxicity at low micromolar concentrations.